Functionalized polymer, rubber composition and pneumatic tire

ABSTRACT

There is disclosed a functionalized elastomer of formula I 
     
       
         
         
             
             
         
       
     
     where R 1 , R 2  and R 3  are independently C1 to C8 alkyl or C1 to C8 alkoxy, with the proviso that at least two of R 1 , R 2  and R 3  are C1 to C8 alkoxy; R 4  is C1 to C8 alkanediyl, C1 to C8 arylene, C1 to C8 alkylarylene, C1 to C8 arylalkanediyl, or a covalent bond; R 5  is C2 alkanediyl; Si is silicon; X is sulfur or oxygen; and P is a diene based elastomer, and n is 1 or 2.

BACKGROUND OF THE INVENTION

Metals from Groups I and II of the periodic table are commonly used toinitiate the polymerization of monomers into polymers. For example,lithium, barium, magnesium, sodium, and potassium are metals that arefrequently utilized in such polymerizations. Initiator systems of thistype are of commercial importance because they can be used to producestereo regulated polymers. For instance, lithium initiators can beutilized to initiate the anionic polymerization of isoprene intosynthetic polyisoprene rubber or to initiate the polymerization of1,3-butadiene into polybutadiene rubber having the desiredmicrostructure.

The polymers formed in such polymerizations have the metal used toinitiate the polymerization at the growing end of their polymer chainsand are sometimes referred to as living polymers. They are referred toas living polymers because their polymer chains which contain theterminal metal initiator continue to grow or live until all of theavailable monomer is exhausted. Polymers that are prepared by utilizingsuch metal initiators normally have structures which are essentiallylinear and normally do not contain appreciable amounts of branching.

Rubbery polymers made by living polymerization techniques are typicallycompounded with sulfur, accelerators, antidegradants, a filler, such ascarbon black, silica or starch, and other desired rubber chemicals andare then subsequently vulcanized or cured into the form of a usefularticle, such as is tire or a power transmission belt. It has beenestablished that the physical properties of such cured rubbers dependupon the degree to which the filler is homogeneously dispersedthroughout the rubber. This is in turn related to the level of affinitythat filler has for the particular rubbery polymer. This can be ofpractical importance in improving the physical characteristics of rubberarticles which are made utilizing such rubber compositions. For example,the rolling resistance and traction characteristics of tires can beimproved by improving the affinity of carbon black and/or silica to therubbery polymer utilized therein. Therefore, it would be highlydesirable to improve the affinity of a given rubbery polymer forfillers, such as carbon black and silica.

In tire tread formulations, better interaction between the filler andthe rubbery polymer results in lower hysteresis and consequently tiresmade with such rubber formulations have lower rolling resistance. Lowtan delta values at 60° C. are indicative of low hysteresis andconsequently tires made utilizing such rubber formulations with low tandelta values at 60° C. normally exhibit lower rolling resistance. Betterinteraction between the filler and the rubbery polymer in tire treadformulations also typically results higher tan delta values at 0° C.which is indicative of better traction characteristics.

The interaction between rubber and carbon black has been attributed to acombination of physical absorption (van der Waals force) andchemisorption between the oxygen containing functional groups on thecarbon black surface and the rubber (see D. Rivin, J. Aron, and A.Medalia, Rubber Chem. & Technol. 41, 330 (1968) and A. Gessler, W. Hess,and A Medalia, Plast. Rubber Process, 3, 141 (1968)). Various otherchemical modification techniques, especially for styrene-butadienerubber made by solution polymerization (S-SBR), have also been describedfor reducing hysteresis loss by improving polymer-filler interactions.In one of these techniques, the solution rubber chain end is modifiedwith aminobenzophenone. This greatly improves the interaction betweenthe polymer and the oxygen-containing groups on the carbon black surface(see N. Nagata, Nippon Gomu Kyokaishi, 62, 630 (1989)). Tin coupling ofanionic solution polymers is another commonly used chain endmodification method that aids polymer-filler interaction supposedlythrough increased reaction with the quinone groups on the carbon blacksurface. The effect of this interaction is to reduce the aggregationbetween carbon black particles which in turn, improves dispersion andultimately reduces hysteresis.

SUMMARY OF THE INVENTION

The subject invention provides a low cost means for the end-groupfunctionalization of rubbery living polymers to improve their affinityfor fillers, such as carbon black and/or silica. Such functionalizedpolymers can be beneficially used in manufacturing tires and otherrubber products where improved polymer/filler interaction is desirable.In tire tread compounds this can result in lower polymer hysteresiswhich in turn can provide a lower level of tire rolling resistance.

The present invention more specifically is directed to a functionalizedelastomer of formula I

where R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8 alkoxy,with the proviso that at least to of R¹, R² and R³ are C1 to C8 alkoxy;R⁴ is C1 to C8 alkanediyl, C1 to C8 arylene, C1 to C8 alkylarylene, C1to C8 arylalkanediyl or a covalent bond; R⁵ is C2 alkanediyl; Si issilicon; X is sulfur or oxygen; and P is a diene based elastomer, and nis 1 or 2.

There is further disclosed a rubber composition comprising thefunctionalized elastomer, and a pneumatic tire comprising the rubbercomposition, and a method of making the functionalized elastomer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of GPC distribution of different polymer samples.

FIG. 2 is a graph of G′, G″ and tan delta versus strain fornonproductive samples with silane coupling agent.

FIG. 3 is a graph of G′, G″ and tan delta versus strain fornon-productive samples without silane coupling agent.

FIG. 4 is a cure curve obtained at 7% strain for productive batches withsilane coupling agent

FIG. 5 is a graph of G′, G″ and tan delta versus strain for productivesamples with silane coupling agent.

FIG. 6 is a cure curve obtained at 7% strain for productive batcheswithout silane coupling agent.

FIG. 7 is a graph of G′, G″ and tan delta versus strain for productivesamples without silane coupling agent.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a functionalized elastomer of formula I

where R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8 alkoxy,with the proviso that at least two of R¹, R² and R³ are C1 to C8 alkoxy;R⁴ is C1 to C8 alkanediyl, C1 to C8 arylene, C1 to C8 alkylarylene, C1to C8 arylalkanediyl, or a covalent bond; R⁵ is C2 alkanediyl; Si issilicon; X is sulfur or oxygen; and P is a diene based elastomer, and nis 1 or 2.

In one embodiment, X is sulfur, R¹, R² and R³ are ethoxy groups and R4is ethanediyl.

In one embodiment, n is 1.

In one embodiment, n is 2.

In one embodiment, P is derived from at least one diene monomer andoptionally at least one vinyl aromatic monomer.

In one embodiment, P is derived from at least one of isoprene andbutadiene, and optionally from styrene.

In one embodiment, P is derived from butadiene and styrene.

There is further disclosed a rubber composition comprising thefunctionalized elastomer, and a pneumatic tire comprising the rubbercomposition, and a method of making the functionalized elastomer.

The subject invention provides a functionalized polymer and a method forthe end-group functionalization of rubbery living polymers to improvetheir affinity for fillers, such as carbon black and/or silica. Theprocess of the present invention can be used to functionalize any livingpolymer which is terminated with a metal of group I or II of theperiodic table. These polymers can be produced utilizing techniques thatare well known to persons skilled in the art. The metal terminatedrubbery polymers that can be functionalized with first and secondterminators in accordance with this invention can be made utilizingmonofunctional initiators having the general structural formula P-M,wherein P represents a diene based elastomer polymer chain and wherein Mrepresents a metal of group I or II. The metal initiators utilized inthe synthesis of such metal terminated polymers can also bemultifunctional organometallic compounds. For instance, difunctionalorganometallic compounds can be utilized to initiate suchpolymerizations. The utilization of such difunctional organometalliccompounds as initiators generally results in the formation of polymershaving the general structural formula M-P-M, wherein P represents adiene based elastomer polymer chain and wherein M represents a metal ofgroup I or II. Such polymers which are terminated at both of their chainends with a metal from group I or II also can be reacted with first andsecond terminators to functionalize both of their chain ends. It isbelieved that utilizing difunctional initiators so that both ends of thepolymers chain can be functionalized with the terminators can furtherimprove interaction with fillers, such as carbon black and silica.

The initiator used to initiate the polymerization employed insynthesizing the living rubbery polymer that is functionalized inaccordance with this invention is typically selected from the groupconsisting of barium, lithium, magnesium, sodium, and potassium. Lithiumand magnesium are the metals that are most commonly utilized in thesynthesis of such metal terminated polymers (living polymers). Normally,lithium initiators are more preferred.

Organolithium compounds are the preferred initiators for utilization insuch polymerizations. The organolithium compounds which are utilized asinitiators are normally organo monolithium compounds. The organolithiumcompounds which are preferred as initiators are monofunctional compoundswhich can be represented by the formula: R—Li, wherein R represents ahydrocarbyl radical containing from 1 to about 20 carbon atoms.Generally, such monofunctional organolithium compounds will contain from1 to about 10 carbon atoms. Some representative examples of preferredbutyllithium, secbutyllithium, n-hexyllithium, n-octyllithium,tertoctyllithium, n-decyllithium, phenyllithium, 1-naphthyllithium,4-butylphenyllithium, p-tolyllithium, 4-phenylbutyllithium,cyclohexyllithium, 4-butylcyclohexyllithium, and4-cyclohexylbutyllithium. Secondary butyllithium is a highly preferredorganolithium initiator. Very finely divided lithium having an averageparticle diameter of less than 2 microns can also be employed as theinitiator for the synthesis of living rubbery polymers that can befunctionalized with first and second terminators in accordance with thisinvention. U.S. Pat. No. 4,048,420, which is incorporated herein byreference in its entirety, describes the synthesis of lithium terminatedliving polymers utilizing finely divided lithium as the initiator.Lithium amides can also be used as the initiator in the synthesis ofliving polydiene rubbers (see U.S. Pat. No. 4,935,471 the teaching ofwhich are incorporated herein by reference with respect to lithiumamides that can be used as initiators in the synthesis of living rubberypolymer).

The amount of organolithium initiator utilized will vary depending uponthe molecular weight which is desired for the rubbery polymer beingsynthesized as well as the precise polymerization temperature which willbe employed. The precise amount of organolithium compound required toproduce a polymer of a desired molecular weight can be easilyascertained by persons skilled in the art. However, as a general rulefrom 0.01 to 1 phm (parts per 100 parts by weight of monomer) of anorganolithium initiator will be utilized. In most cases, from 0.01 to0.1 phm of an organolithium initiator will be utilized with it beingpreferred to utilize 0.025 to 0.07 phm of the organolithium initiator.

Many types of unsaturated monomers which contain carbon-carbon doublebonds can be polymerized into polymers using such metal catalysts.Elastomeric or rubbery polymers can be synthesized by polymerizing dienemonomers utilizing this type of metal initiator system. The dienemonomers that can be polymerized into synthetic rubbery polymers can beeither conjugated or nonconjugated diolefins. Conjugated diolefinmonomers containing from 4 to 8 carbon atoms are generally preferred.Vinyl-substituted aromatic monomers can also be copolymerized with oneor more diene monomers into rubbery polymers, for examplestyrene-butadiene rubber (SBR). Some representative examples ofconjugated diene monomers that can be polymerized into rubbery polymersinclude 1,3-butadiene, isoprene, 1,3-pentadiene,2,3-dimethyl-1,3-butadiene, 2-methyl1,3-pentadiene,2,3-dimethyl-1,3-pentadiene, 2-phenyl-1,3-butadiene, and4,5-diethyl-1,3-octadiene. Some representative examples ofvinyl-substituted aromatic monomers that can be utilized in thesynthesis of rubbery polymers include styrene, 1-vinylnapthalene,3-methylstyrene, 3,5-diethylstyrene, 4-propylstyrene,2,4,6-trimethylstyrene, 4-dodecylstyrene,3-methyl-5-normal-hexylstyrene, 4-phenylstyrene,2-ethyl-4-benzylstyrene, 3,5-diphenylstyrene, 2,3,4,5-tetraethylstyrene,3-ethyl-1-vinylnapthalene, 6-isopropyl-1-vinylnapthalene,6-cyclohexyl-1-vinylnapthalene, 7-dodecyl-2-vinylnapthalene,α-methylstyrene, and the like.

The metal terminated rubbery polymers that are functionalized with firstand second terminators in accordance with this invention are generallyprepared by solution polymerizations that utilize inert organicsolvents, such as saturated aliphatic hydrocarbons, aromatichydrocarbons, or ethers. The solvents used in such solutionpolymerizations will normally contain from about 4 to about 10 carbonatoms per molecule and will be liquids under the conditions of thepolymerization. Sonic representative examples of suitable organicsolvents include pentane, isooctane, cyclohexane, normal-hexane,benzene, toluene, xylene, ethylbenzene, tetrahydrofuran, and the like,alone or in admixture. For instance, the solvent can be a mixture ofdifferent hexane isomers. Such solution polymerizations result in theformation of a polymer cement (a highly viscous solution of thepolymer).

The metal terminated living rubbery polymers utilized in the practice ofthis invention can be of virtually any molecular weight. However, thenumber average molecular weight of the living rubbery polymer willtypically be within the range of about 50,000 to about 500,000. It ismore typical for such living rubbery polymers to have number averagemolecular weights within the range of 100,000 to 250,000.

The functionalized elastomer is formed by reacting the metal terminatedliving rubbery polymer with two terminators in a cascading reaction,that is, P-M or M-P-M is reacted with a first terminator, followed byreaction with a second terminator, in a sequential, two-reaction cascadeas shown in scheme 1. In the first termination reaction, the metalterminated living rubber polymer (indicated as P-M) is reacted with afirst terminator. Suitable first terminators include ethylene sulfide,ethylene oxide, or more generally a first terminator of formula II

wherein, X is sulfur or oxygen

In the second termination reaction, the product of the first terminationreaction is reacted with a second terminator of formula III

wherein R¹, R², R³ and R⁴ are as define as for formula I, and Q is ahalogen. In one embodiment. Q is chlorine. One example of suitablesecond terminator is chlorotriethoxysilane.

The metal terminated living rubbery polymer can be functionalized bysimply adding a stoichiometric amounts of the first and secondterminators, with the first terminator added to a solution of therubbery polymer (a rubber cement of the living polymer), followed byaddition to the second terminator following the first terminationreaction. In other words, approximately one mol of each of the first andsecond terminators is added per mole of terminal metal groups in theliving rubbery polymer. The number of moles of metal end groups in suchpolymers is assumed to be the number of moles of the metal utilized inthe initiator. It is, of course, possible to add greater than astoichiometric amount of the first and second terminators. However, theutilization of greater amounts is not beneficial to final polymerproperties. Nevertheless, in many cases it will be desirable to utilizea slight excess of the first and second terminators to insure that atleast a stoichiometric amount is actually employed or to control thestoichiometric of the functionalization reaction. In most cases fromabout 0.8 to about 1.1 mol of the first and second terminators will beutilized per mole of metal end groups in the living polymer beingtreated. In the event that it is not desired to functionalize all of themetal terminated chain ends in a rubbery polymer then, of course, lesseramounts of the first and second terminators can be utilized.

The first and second terminators will react with the metal terminatedliving rubbery polymer over a very wide temperature range. For practicalreasons the functionalization of such living rubbery polymers willnormally be carried out at a temperature within the range of 0° C. to150° C. In order to increase reaction rates, in most cases it will bepreferred to utilize a temperature within the range of 20° C. to 100° C.with temperatures within the range of 50° C. to 80° C. being mostpreferred. The capping reaction is very rapid and only very shortreaction times within the range of 0.5 to 4 hours are normally required.However, in some cases reaction times of up to about 24 hours may beemployed to insure maximum conversions.

After the functionalization reaction is completed, it will normally bedesirable to “kill” any living polydiene chains which remain. This canbe accomplished by adding an alcohol, such as methanol or ethanol, tothe polymer cement after the functionalization reaction is completed inorder to eliminate any living polymer that was not consumed by thereaction with the first and second terminators. The end-groupfunctionalized polydiene rubber can then be recovered from the solutionutilizing standard techniques.

The functionalized polymer may be compounded into a rubber composition.

The rubber composition may optionally include, in addition to thefunctionalized polymer, one or more rubbers or elastomers containingolefinic unsaturation. The phrases “rubber or elastomer containingolefinic unsaturation” or “diene based elastomer” are intended toinclude both natural rubber and its various raw and reclaim forms aswell as various synthetic rubbers. In the description of this invention,the terms “rubber” and “elastomer” may be used interchangeably, unlessotherwise prescribed. The terms “rubber composition,” “compoundedrubber” and “rubber compound” are used interchangeably to refer torubber which has been blended or mixed with various ingredients andmaterials and such terms are well known to those having skill in therubber mixing or rubber compounding art. Representative syntheticpolymers are the homopolymerization products of butadiene and itshomologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile (which polymerize with butadiene to formNBR), methacrylic acid and styrene, the latter compound polymerizingwith butadiene to form SBR, as well as vinyl esters and variousunsaturated aldehydes, ketones and ethers, e.g., acrolein methylisopropenyl ketone and vinylethyl ether. Specific examples of syntheticrubbers include neoprene (polychloroprene), polybutadiene (includingcis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene),butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutylrubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadieneor isoprene with monomers such as styrene, acrylonitrile and methylmethacrylate, as well as ethylene/propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. Additional examples ofrubbers which may be used include alkoxy-silyl end functionalizedsolution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupledand tin-coupled star-branched polymers. The preferred rubber orelastomers are polyisoprene (natural or synthetic), polybutadiene andSBR.

In one aspect the at least one additional rubber is preferably of atleast two of diene based rubbers. For example, a combination of two ormore rubbers is preferred such as cis 1,4-polyisoprene rubber (naturalor synthetic, although natural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrene/butadiene (E-SBR) might be used having as relativelyconventional styrene content of about 20 to about 28 percent boundstyrene or, for some applications, an E-SBR having a medium torelatively high bound styrene content, namely, a bound styrene contentof about 30 to about 45 percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent houndacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrene/butadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used. SuchBR can be prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The rubber composition may also include up to 70 phr of processing oil.Processing oil may be included in the rubber composition as extendingoil typically used to extend elastomers. Processing oil may also beincluded in the rubber composition by addition of the oil directlyduring rubber compounding. The processing oil used may include bothextending oil present in the elastomers, and process oil added duringcompounding. Suitable process oils include various oils as are known inthe art, including aromatic, paraffinic, naphthenic, vegetable oils, andlow PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils.Suitable low PCA oils include those having a polycyclic aromatic contentof less than 3 percent by weight as determined by the IP346 method.Procedures for the IP346 method may be found in Standard Methods forAnalysis & Testing of Petroleum and Related Products and BritishStandard 2009 Parts, 2003, 62nd edition, published by the Institute ofPetroleum, United Kingdom.

The rubber composition may include from about 10 to about 150 phr ofsilica. In another embodiment, from 20 to 80 phr of silica may be used.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas. In one embodiment,the BET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about So to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc; silicas available from Rhodia, with, for example, designationsof Z1165MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler inan amount ranging from 10 to 150 phr. In another embodiment, from 20 to80 phr of carbon black may be used. Representative examples of suchcarbon blacks include N110, N121, N134, N220, N231, N234, N242, N293,N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539,N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907,N908, N990 and N991. These carbon blacks have iodine absorptions rangingfrom 9 to 145 g/kg and DBP number ranging from 34 to 150 cm³/100 g.

Other fillers may be used in the rubber composition including, but notlimited to, particulate fillers including ultra high molecular weightpolyethylene (UHMWPE), crosslinked particulate polymer gels includingbut not limited to those disclosed in U.S. Pat. Nos. 6,242,534;6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, andplasticized starch composite filler including but not limited to thatdisclosed in U.S. Pat. No. 5,672,639. Such other fillers may be used inan amount ranging from 1 to 30 phr.

In one embodiment the rubber composition may contain a conventionalsulfur containing organosilicon compound. In one embodiment, the sulfurcontaining organosilicon compounds are the 3,3′-bis(trimethoxy ortrietboxy silylpropyl)polysulfides. In one embodiment, the sulfurcontaining organosilicon compounds are3,3′-bis(triethoxysilylpropyl)disulfide and/or3,3′-bis(triethoxysilylpropyl)tetrasulfide.

In another embodiment, suitable sulfur containing organosiliconcompounds include compounds disclosed in U.S. Pat. No. 6,608,125. In oneembodiment, the sulfur containing organosilicon compounds includes3-(octanoylthio)-1-propyltriethoxysilane,CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commerciallyas NXT™ from Momentive Performance Materials.

In another embodiment, suitable sulfur containing organosiliconcompounds include those disclosed in U.S. Patent Publication No.2003/0130535. In one embodiment, the sulfur containing organosiliconcompound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubbercomposition will vary depending on the level of other additives that areused. Generally speaking, the amount of the compound will range from 0.5to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Representative examples of sulfur donors include elementalsulfur (free sulfur), an amine disulfide, polymeric polysulfide andsulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agentis elemental sulfur. The sulfur-vulcanizing agent may be used in anamount ranging from 0.5 to 8 phr, alternatively with a range of from 1.5to 6 phr. Typical amounts of tackifier resins, if used, comprise about0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in The Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. In one embodiment, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely, at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 140° C. and 190° C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions, and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

The rubber composition may be incorporated in a variety of rubbercomponents of the tire. For example, the rubber component may be a tread(including tread cap and tread base), sidewall, apex, chafer, sidewallinsert, wirecoat or innerliner. In one embodiment, the component is atread.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire, and the like. In one embodiment, the tire is a passenger ortruck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

This invention is illustrated by the following examples that are merelyfor the purpose of illustration and are not to be regarded as limitingthe scope of the invention or the manner in which it can be practiced.Unless specifically indicated otherwise, parts and percentages are givenby weight.

EXAMPLE 1 Co-Polymerization of Styrene and Butadiene

Polymerizations were done in 1 gallon reactor at 65° C. Monomer premixof styrene and butadiene was charged into reactor followed by additionof modifier (TMEDA) and initiator (n-butyl lithium). When conversion wasabove 98%, the polymerization was terminated with isopropanol orterminating first with ES followed by chlorotriethoxysilane in a cascadereaction. Polymer samples were also synthesized in which termination wasdone using either ethylene sulfide or chlorotriethoxysilane to seeadvantage of having functionality from both terminating agent togetherthan individual.

The synthesis of functionalized polymer as well as control was done in a1 gallon hatch reactor. The polymer obtained was characterized (GPCresults shown in Table 2 and Mooney, FT-IR and DSC results are shown inTable 3) using different techniques, for example, GPC for determinationof molecular weight (GPC distribution of different polymer samples isshown in FIG. 1), DSC for determination of Tg, IR for determining cis,trans, styrene and vinyl content, and Mooney viscosity measurements.

TABLE 2 GPC characterization of different polymer samples Overall MnPolymer Sample (g/mol) PDI 1: Functionalized SBR¹ (Comparative) 250,0001.42 2: Non-functionalized SBR² (Control) 181,000 1.03 3: ESfunctionalized SBR³ 197,000 1.10 4: CTES functionalized SBR⁴ 249,0001.14 5: ES&CTES functionalized SBR⁵ 206,000 1.18 ¹Functionalizedsolution polymerized styrene-butadiene rubber, as Sprintan ® SLR 4602available commercially from Styron. ²Solution polymerizedstyrene-butadiene rubber terminated using isopropanol. ³Solutionpolymerized styrene-butadiene terminated with ethylene sulfide (ES)⁴Solution polymerized styrene-butadiene terminated withchlorotriethoxysilane (CTES) ⁵Solution polymerized styrene-butadieneterminated with ethylene sulfide and chlorotriethoxysilane

TABLE 3 Mooney, FT-IR and DSC characterization of different polymersamples Tg Polymer Sample Mooney Cis Trans Styrene Vinyl (° C.) 1:Functionalized 65 12.15 21.88 17.97 48 −25.0 SBR¹ (Comparative) 2:Non-functionalized 35.9 13.07 18.29 23.70 44.9 −22.08 SBR² (Control) 3:ES functionalized 32.4 12.89 18.34 23.46 45.31 −22.09 SBR³ 4: CTES 32.512.79 18.55 23.73 44.93 −22.00 functionalized SBR⁴ 5. ES and CTES 39.712.94 17.96 25.44 43.65 −22.41 functionalized SBR⁵ ¹Functionalizedsolution polymerized styrene-butadiene rubber, as Sprintan ® SLR 4602available commercially from Styron. ²Solution polymerizedstyrene-butadiene rubber terminated using isopropanol. ³Solutionpolymerized styrene-butadiene terminated with ethylene sulfide ⁴Solutionpolymerized styrene-butadiene terminated with chlorotriethoxysilane⁵Solution polymerized styrene-butadiene terminated with ethylene sulfideand chlorotriethoxysilane

EXAMPLE 2 Mixing Studies and Compound Testing

The functionalized sSBR (functionalized using ES, CTES and both ES&CTESas well as control (non-functionalized SBR) and comparativefunctionalized SBR) were mixed with silica and oil in a 3-piece 75 mL CWBrabender® mixer equipped with Banbury® rotors.

sSBR samples were mixed with additives in a three stage mix procedure asshown in Table 3, with all amounts given in parts by weight, per 100parts by weight of elastomer (phr). In the first non-productive mixstage, compounds were mixed for 4 minutes at 60 rpm using 140° C. asstarting temperature. All compounds were pressed in a compressionmolding machine for 1 minute before a second non-productive mix stage.In the second non productive step mixing conditions were the same as inthe first non-productive step, with mix time of 3 minutes. Productivemixes were carried out using 60° C. starting temperature and 60 rpm withmix time of 3 minute.

TABLE 3 Formulation used for mixing Variable¹ (Addition as indicated inExamples 3-6) Silane coupling agent 5.2 (phr) First Non Productive StepSBR 100 Silica 65 (phr) Oil 30 (phr) Stearic Acid 2 (phr) Zinc Oxide 3.5(phr) Second Non Productive Step Remixing Productive Mix Step Sulfur 1.7(phr) Accelerators 3.1 (phr) Antidegradant 0.75 (phr) ¹Silane coupling,when used, was added during the first non productive step;

The compounds were tested for silica interaction using an RPA 2000® fromAlpha Technology. Green (non-productive) compounds were first heated to160° C. and the torque increase was monitored as a function of timeusing 1 Hz and 0.48% strain in order to determine the rate of the filler“flocculation”. Subsequently the compounds were cooled to 40° C. and astrain sweep was carried out using 1 in order to determine the Payneeffect, i.e., the strain dependence of G′, G″ and tan delta. Cure wascarried out at 160° C. using 7% strain. Cured compounds dynamicproperties were measured first by curing the sample at 160° C. for 30minute at the lowest possible strain to mimic a static cure. After thissamples were cooled and tested in the given manner for non-productivecompounds.

EXAMPLE 3

Samples 6-10 were prepared according to Table 3 as non-productivecompounds with added silane coupling agent, with no productive mix step.

FIG. 2 shows the results of the strain sweeps conducted at 40° C. on thenon-productive compounds with silane coupling agent after 30 minutesheat treatment of the samples at low strain at 160° C. in the RPA. Asshown in FIG. 2, G′ and tan delta of non-functionalized control sampleshows highest strain dependency. The functionalized polymer(Comparative) sample shows lowest strain dependency. ES&CTESfunctionalized polymer samples shows reduced strain dependency, howeverthese polymers have higher tan delta values as compared to Comparative.

The ratio of the low amplitude (0.48% strain) modulus (LAM) and highamplitude (100% strain) modulus (HAM) which is a measure of the Payneeffect and is given in Table 4 for the various samples. Higher theLAM/HAM ratio less is polymer-filler interaction. As seen in Table 4,non-functionalized control polymer Sample 2 shows highest LAM/HAM valueindicating least polymer-filler interaction, Comparative shows Loweststrain dependency and other functionalized polymer are in betweenComparative and non-functionalized.

TABLE 4 LAM/HAM ratios and tan delta at 5% strain for non- productivebatches with silane coupling agent Tan Delta (40° C.) SBR Sample LAM/HAM(5% strain) 1 6 (Comparative) 7.2 0.19 2 7 (Control) 18.9 0.26 3 8(ES)11.3 0.23 4 9(CTES) 12.9 0.25 5 10(ES&CTES) 11.6 0.24

EXAMPLE 4

Samples 11-15 were prepared according to Table 3 as non-productivecompounds without any silane coupling agents

FIG. 3 shows the results of the strain sweeps conducted at 40° C. on thenon-productive compounds without any silane coupling agent after 30minutes heat treatment of the samples at low strain at 160° C. in theRPA. In this case no coupling agent was added to evaluate solelyinteraction between polymer chain ends and filler. In this case,non-functionalized as well as all other functionalized polymer samplesshowed highest strain dependency. Comparative Sample 1 (Comparative)shows reduced strain dependency.

The ratio of the to amplitude (0.48% strain) and high amplitude (100%strain) moduli is shown in Table 5. Without the use of slime couplingagent, Payne effect is enhanced as compared to Payne effect observedwith the use of silane coupling agent. The control and all otherfunctionalized polymers show highest LAM/HAM value, i.e., relativelyhigh Payne effect. Comparative shows lowest Payne while ES, CTES andES&CTES functionalized polymers shows lower Payne effect compared tonon-functionalized polymer. As the result of higher Payne effect, tandelta values for control and other functionalized polymers are higherthan Comparative.

TABLE 5 LAM/HAM ratios and tan delta at 5% strain for non- productivebatches without silane coupling agent Tan Delta (40° C.) SBR Sample No.LAM/HAM (5% strain) 1 11(Comparative) 17.5 0.22 2 12(Control) 53.8 0.433 13(ES) 49.7 0.35 4 14(CTES) 46.2 0.35 5 15(ES&CTES) 45.9 0.35

EXAMPLE 5

Samples 16-20 were prepared according to Table 3 as productivecompounds, with addition of silane in productive mix step.

After non-productive batches, the addition of silane in productive batchis illustrated. Compound mixing was done with a first non-productive mixstage followed by the second non-productive step and finally productivestep. Addition of the silane coupling agent was done in the firstnon-productive mix stage.

The cure curves obtained with silane coupling agent at 7% strain isshown in FIG. 4. Cure parameters max torque S′max and change in torquedelta S′ are given in Table 6.

TABLE 6 Maximum and delta torque values for productive batches withsilane coupling agent SBR Sample No. S′max (dN*m) Delta S′ (dN*m) 116(Comparative) 11.18 9.08 2 17(Control) 15.7 14.56 3 18(ES) 16.8 15.564 19(CTES) 14.54 13.44 5 20(ES&CTES) 14.79 13.37

The strain sweeps were conducted in separate RPA runs. In these runs thesamples were cured at 160° C. for 30 minutes using the lowest possiblestrain (0.28%) in order to mimic static cure and not to alterfiller-filler or filler-polymer interaction. Strain sweep cures wereobtained at 40° C. as shown in FIG. 5.

The ratio of the low amplitude (0.48% strain) and high amplitude (100%strain) moduli is shown in Table 7. The strain sweeps conducted on thecured compounds indicates that functionalized polymer based on ES, CTESand ES & CTES shows Payne effect higher than Comparative but lower thannon-functionalized polymer sample indicating lower polymer-fillerinteraction than Comparative but better than non-functionalized.

EXAMPLE 6

In this example, mixing of productive compound without addition ofsilane is illustrated. Samples 21-25 were prepared according to Table 3as productive compound without addition of silane. Compound mixing wasdone similar to one used for productive batches with silane couplingagent. The cure curve for productive sample without silane couplingagent at 7% strain is shown in FIG. 6. Cure parameters max torque S′maxand change in torque delta S′ are given in Table 8.

TABLE 7 LAM/HAM ratios and tan delta at 5% strain for productive batcheswith silane coupling agent Tan Delta Tan Delta (30° C.) (40° C.) (10%strain) SBR Sample No. LAM/HAM (5% strain) ARES strain sweep 116(Comparative) 3.2 0.14 0.15 2 17(Control) 4.8 0.18 0.18 3 18(ES) 4.10.17 0.15 4 19(CTES) 3.8 0.17 0.16 5 20(ES&CTES) 3.4 0.17 0.15

TABLE 8 Maximum and delta torque values for productive batches withoutsilane coupling agent SBR Sample No. S′max (dN*m) Delta S′ (dN*m) 121(Comparative) 25.42 13.99 2 22(Control) 24.72 18.21 3 23(ES) 23.9517.74 4 24(CTES) 25.78 18.90 5 25(ES&CTES) 25.9 18.21

The strain sweeps were conducted in separate RPA runs. In these runs,the sample were cured at 160° C. for 30 minutes using the lowestpossible strain (0.28%) in order to mimic static cure and not to alterfiller-filler or filler-polymer interaction. The ratio of the lowamplitude (0.48% strain) and high amplitude (100% strain) moduli isshown in Table 9. Strain sweep curves were obtained at 40° C. as shownin FIG. 7.

TABLE 9 LAM/HAM ratios and tan delta at 5% strain for productive batcheswithout silane coupling agent Tan Delta Tan Delta (30° C.) (40° C.) (10%Strain) SBR Sample No. LAM/HAM (5% strain) ARES strain sweep 121(Comparative) 8.7 0.13 0.18 2 22(Control) 16.2 0.21 0.18 3 23(ES) 14.70.20 0.17 4 24(CTES) 14.5 0.19 0.19 5 25(ES&CTES) 14.9 0.18 0.18

The strain sweeps conducted on the cured compounds indicates ES, CTESand ES&CTES functionalized polymer does shows reduction in Payne effectas compared to non-functionalized polymers.

The use of ethylene sulfide and chlorotriethoxysilane leads to synthesisof siloxy terminated polymers which can have interaction with silicaduring compounding. Functionalized polymer used on ES and CTES carries asulfur group which is protected with silane. ES&CTES functionalizedpolymer, polymer chain can interact with silica with siloxy groups,however during compounding some of sulfur-silane bonds can potentiallycleave off generating thiol groups. Thiol groups which will be generatedon polymer chain as the result of cleavage can help in cross-linkingpolymer chains. Non-functionalized polymer was synthesized as control toobserve difference in behavior of functionalized versusnon-functionalized polymers in their interaction with silica.Non-functionalized polymer sample showed highest Payne effect in allcases which means lowest interaction with silica as there are nofunctional group which can interact with silica. However, reduction inPayne effect is observed when coupling agent is used.

While certain representative embodiments and details have been shown forthe purpose of illustrating the subject invention, it will be apparentto those skilled in this art that various changes and modifications canbe made therein without departing from the scope of the subjectinvention.

What is claimed is:
 1. A functionalized elastomer of formula I

where R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8 alkoxy,with the proviso that at least two of R¹, R² and R³ are C1 to C8 alkoxy;R⁴ is C1 to C8 alkanediyl, C1 to C8 arylene, C1 to C8 alkylarylene, C1to C8 arylalkanediyl, or a covalent bond; R⁵ is C2 alkanediyl; Si issilicon; X is sulfur or oxygen; and P is a diene based elastomer, and nis 1 or
 2. 2. The functionalized elastomer of claim 1, wherein R¹, R²and R³ are each C1 to C8 alkoxy.
 3. The functionalized elastomer ofclaim 1, wherein n is
 1. 4. The functionalized elastomer of claim 1,wherein n is
 2. 5. The functionalized elastomer of claim 1, wherein P isderived from at least one diene monomer and optionally at least onevinyl aromatic monomer.
 6. The functionalized elastomer of claim 1,wherein P is derived from at least one of isoprene and butadiene, andoptionally from styrene.
 7. The functionalized elastomer of claim 1,wherein P is derived from butadiene and styrene.
 8. The functionalizedelastomer of claim 1, wherein X is sulfur, R¹, R² and R³ are ethoxygroups, R⁴ is C0 and R⁵ is ethanediyl.
 9. A rubber compositioncomprising the functionalized elastomer of claim
 1. 10. The rubbercomposition of claim 10, further comprising silica.
 11. A pneumatic tirecomprising the rubber composition of claim
 11. 12. A method of making afunctionalized elastomer, comprising the steps of A) reacting a metalterminated diene based elastomer living polymer with a first terminatorselected from the group consisting of ethylene sulfide or ethylene oxideto form a first terminated polymer; and B) reacting the first terminatedpolymer with a second terminator of formula III

wherein R¹, R² and R³ are independently C1 to C8 alkyl or C1 to C8alkoxy, with the proviso that at least two of R¹, R² and R³ are C1 to C8alkoxy; R⁴ is C1 to C8 alkanediyl, C1 to C8 arylene, C1 to C8alkylarylene, C1 to C8 arylalkanediyl, or a covalent bond; and Q is ahalogen.
 13. The method of claim 12, wherein the first terminator isethylene sulfide.
 14. The method of claim 12, wherein the secondterminator is chlorotriethoxysilane.
 15. The method of claim 12, whereinthe diene based elastomer is derived from at least one diene monomer andoptionally at least one vinyl aromatic monomer.
 16. The method of claim12, wherein the diene based elastomer is derived from at least one ofisoprene and butadiene, and optionally from styrene.
 17. The method ofclaim 12, wherein the diene based elastomer is derived from butadieneand styrene.